The existing methods of constructing wind towers vary depending on whether the materials are steel or concrete. The decision process used to select steel or concrete depends on the geographic location, regional resources and access to the wind farm site. Steel wind towers are commonly built through bolting of steel tubular sections together at intermediate flanges. The heights of steel towers are often limited by the diameter of the steel tubular sections that can be physically transported from the location of the steel fabricator to the wind farm site without significant modifications to existing roads, bridges, rail infrastructure, hauling equipment and other physical constraints. These limitations typically result in steel member diameters to approximately 20 ft., which in turn limits the tower height to approximately 300 ft. using conventional strength steel. Energy production from a wind tower has been typically shown to increase by increasing the height of the tower as a result of improved consistency in laminar wind flow. To increase the height of steel towers, some developers are installing concrete pedestals underneath the base of the steel tower.
Concrete towers being constructed today by using precast methods and cast in place methods. The advantages of concrete towers are they can be constructed using regional labor and materials and typically do not have height limitations as a result of transportation constraints since these towers can be fully fabricated on site. Cast in place construction methods utilize vertically extending formwork to support the pouring of fresh concrete into the forms at height. Restrictions to this method are the reduced speed of construction and sensitivity to inclement weather. Existing precast concrete techniques commonly precast the elements in a manner that results in vertical and horizontal joints, requiring joining of the elements during construction with grout. In this solution, post-tensioning in both directions can often be required to achieve a durable tower structure.
Other precast solutions involve the grinding of the annular horizontal concrete surfaces to achieve a quality load bearing connection. The segments are commonly precast offsite or nearby to the tower farm. The vertical post-tensioning is commonly located inside the concrete wall where it is anchored. The common geometry of a concrete wind tower is tapered, creating additional complexity in the forming system and placement of reinforcing and post-tensioning geometry. The challenges inherent to the existing steel and concrete tower designs and construction methods are their limitation on geometry in the case of steel towers and the complexity of the concrete towers.